The familiar front-end bearing structure for a passenger car bodywork typically comprises a pair of generally horizontal bottom front longitudinal bearers disposed spaced apart along opposite sides of the vehicle body. Each front longitudinal bearer has an upright bearer mounted along an upper surface thereof for supporting a suspension strut mount at a spaced distance above its respective front longitudinal bearer.
The individual bearer members of the front-end bearing structure of the type described above are typically fabricated from sheet metal parts. The hollow-section bearers, for example, are made from at least two deep-drawn metal sheets which are welded together. The suspension strut mounts, also made from sheet metal parts, are embedded in the bell structure of deep-drawn wheel housings in accordance with the conventional practice. The wheel housings consist of open sheet metal shells which are connected to the underside of the longitudinal bearers. Applied force is guided across the sheet metal elements as thrust walls.
In addition, in the known designs, an auxiliary frame is fastened to the bottom front longitudinal bearers forwardly of the suspension strut mounts to form a compound bearer having front screw fastening points for securing an additional assembly thereto, such as, for example, a front bumper assembly. The result is that the suspension strut mount is a heavily loaded and heavily stressed part of the body structure.
In the conventional sheet metal front end bearing structural designs of the prior art, costly reinforcement measures are needed to achieve the requisite rigidity and stiffness for the bearing structure in this region. Also, the desired bearing structure must ensure a stable support for mounting an auxiliary frame on the bottom longitudinal bearers at the front screw fastening points of the auxiliary frame. This is especially important in order to pass the required crash tests.
The steel sheets used to construct such self-supporting vehicle bodyworks are typically shaped in a deep drawing process. While the dies used for shaping the steel sheets are relatively expensive, they do provide a cost-favorable solution for mass production since they permit large production runs. However, in view of the high investment costs for all the required dies, the aforesaid process is very cost-intensive for smaller production runs.
A more cost-favorable solution for small production runs is known, for example, from European Patent document EP 0 146 716 wherein it is disclosed a vehicle body for a passenger car having a bearing structure comprising of hollow section frame members which are joined together by node connector elements. The hollow section frame members are formed as extruded aluminum sections and the node connector elements are formed as light metal cast pieces. In addition to being a more cost-favorable solution for small production runs, the aluminum bodywork disclosed in EP 0 146 716 is lighter in weight and is more resistant to corrosion than a sheet metal bodywork.
However, the suspension strut mount as well as its support on its respective longitudinal bearer for this design are also fabricated from sheet metal parts in a manner similar to the conventional all sheet metal self-supporting bodywork as described above. Accordingly, similar costly reinforcement measures must also be taken to ensure adequate rigidity and stiffness of the bearing structure in this case.
From Japanese patent document JP-A-2246 877 there is disclosed a reinforced front wheel apron and suspension strut mount arrangement designed as a self-supporting sheet metal structure for improving the rigidity in a front engine compartment in a vehicle bodywork. The reinforced front wheel apron comprises two portions including a first inward portion having a U-shaped cross section and a flat plate-like outer portion. When assembled, the two portions are joined by a welded joint and form a hollow section supporting bearer which extends forwardly in the horizontal direction starting from the A post at an upper edge of the wheel apron and continues to a point in front of the suspension strut mount. From there the hollow section supporting bearer angles downwardly in a substantially vertical direction to join the bottom longitudinal bearer. The metal sheets which form the suspension strut mount also form a brace with this hollow section supporting bearer. In this design each wheel housing is reinforced by sheet metal pieces.
In the arrangement described, a generally triangular framework is formed by the downwardly slanting forwardmost portion of the hollow section supporting bearer, the bottom longitudinal bearer and the upstanding support for the suspension strut mount. This triangular framework, in combination with the additional portion of the hollow section bearer which extends in the rearward longitudinal direction from the upstanding support for the suspension strut mount to the A post, divides and distributes the impact force associated with a frontal collision along the frame members. In particular, a first portion of the impact force is directed through the bottom longitudinal bearer to the door sill and floor region and a second portion of the impact force is directed through the substantially vertically upwardly slanted portion of the hollow section supporting bearer, where it then continues through the suspension strut mount to the upper region of the door column and roof region via the substantially horizontal portion of the hollow section supporting bearer which connects the suspension strut to the A post.
In this design, however, only a small portion of the impact force is absorbed or dissipated by the hollow section supporting bearer portion of the front wheel apron, since it extends in the horizontal direction parallel to the bottom longitudinal bearer over most of its length before it abruptly slants substantially vertically downward to join the bottom longitudinal bearer at its forwardmost end. As a result, the hollow section supporting bearer portion of the front wheel apron is more prone to buckling rather than absorbing impact energy during a frontal collision.
Further, since this document does not disclose or suggest the use of a two piece bottom longitudinal bearer, the problems associated with the interconnection of the multiple portions of a segmented longitudinal bearer are not addressed. Nor is there disclosed or suggested a simple solution for providing a sufficiently stable triangular interconnection of the suspension strut mount, the supporting bearer, and suspension strut bearer. Accordingly, in this design, the fastening point for an auxiliary frame assembly, such as for example a front bumper assembly, must be formed independently of the front bearing structure.